Glossary Item
A contaminated culture is a microbial culture that contains unwanted organisms in addition to the intended species. Contaminants may come from the environment, equipment or human handling and can affect the accuracy of experiments or production processes.
Explanation
In microbiology the goal is often to obtain a pure culture from a single species. During inoculation, incubation or sampling, airborne spores, stray bacteria, moulds or viruses can enter the medium. Contamination can also arise from inadequately sterilised media, faulty seals, unclean instruments or cross‑transfer from other cultures. The presence of foreign organisms alters the growth dynamics, nutrient consumption and appearance of the culture, leading to unreliable results or spoilage. In fermenters, contamination can reduce yield or produce harmful metabolites. Signs of contamination include unexpected turbidity in broth, colonies with unexpected morphology or colour on solid media, odour changes, pH shifts and microscopic detection of cells with different shapes or sizes. In cell culture contamination by bacteria, fungi or mycoplasma may cause medium to turn cloudy or cells to detach and die. Preventing contamination requires proper aseptic techniques: sterilising media and equipment, using disinfectants, flaming loops and needles, minimising opening time of containers, working near a flame or in a laminar‑flow hood and wearing gloves. Disposing of contaminated cultures properly prevents spread of opportunistic pathogens and maintains laboratory safety.
Examples and significance
An agar plate streaked for a bacterial isolate may develop fuzzy patches of mould or pigmented colonies from airborne spores, indicating contamination. Broth cultures of Escherichia coli left uncapped may become cloudy with Bacillus spores from dust. In industrial fermentations for antibiotics or enzymes, contamination by lactobacilli or wild yeasts can outcompete production strains and spoil the batch. In tissue culture laboratories, mycoplasma contamination is a hidden problem that alters gene expression in animal cells. Recognising and avoiding contamination is essential for reliable results, product quality and safety. Related Terms: pure culture, aseptic technique, contamination, sterile, mixed culture